Characterization of phosphonium ionic liquids through a linear solvation energy relationship and their use as GLC stationary phases

In recent years, room temperature ionic liquids (RTILs) have proven to be of great interest to analytical chemists. One important development is the use of RTILs as highly thermally stable GLC stationary phases. To date, nearly all of the RTIL stationary phases have been nitrogen-based (ammonium, pyrrolidinium, imidazolium, etc.). In this work, eight new monocationic and three new dicationic phosphonium-based RTILs are used as gas–liquid chromatography (GLC) stationary phases. Inverse gas chromatography (GC) analyses are used to study the solvation properties of the phosphonium RTILs through a linear solvation energy model. This model describes the multiple solvation interactions that the phosphonium RTILs can undergo and is useful in understanding their properties. In addition, the phosphonium-based stationary phases are used to separate complex analyte mixtures by GLC. Results show that the small differences in the solvent properties of the phosphonium ILs compared with ammonium-based ILs will allow for different and unique separation selectivities. Also, the phosphonium-based stationary phases tend to be more thermally stable than nitrogen-based ILs, which is an advantage in many GC applications.     

Analytical applications of room-temperature ionic liquids: a review of recent efforts

Room-temperature ionic liquids (RTILs) are solvents that may have great potential in chemical analysis. Recent surge in the number of publications/reports/books/monographs clearly indicate an increasing interest of scientific and engineering community toward these exciting and unique solvents. Consequently, a variety of analytical applications of RTILs have started to emerge. This review presents an account of some of the recent reports on RTILs in major subdisciplines of analytical chemistry. Specifically, recent literature representing the applications of RTILs in chromatography, extraction, electroanalytical chemistry, sensing, and spectrometry is reviewed. With a rapid growth in the number of publications on analytical applications of RTILs, it appears that in the near future these neoteric solvents are definitely going to be a permanent feature in analytical chemistry.     

Dynamic stokes shift and excitation wavelength dependent fluorescence of dipolar molecules in room temperature ionic liquids

Room temperature ionic liquids (RTILs) are viscous media consisting entirely of ions. Because of the complex nature of various interactions in these media, the solvent properties of the RTILs are very little understood. Since the fluorescence response of molecules comprising conjugated electron donor and acceptor groups, referred to as dipolar molecules, is one of the most frequently exploited sources of information on complex media, whose properties are largely unknown, it is possible to obtain insight into the structure and dynamics of the RTILs by studying the fluorescence behavior of dipolar solutes in these complex media. The most commonly exploited utility of a fluorescent dipolar system is in the estimation of the polarity of the media from its steady state fluorescence response. While several dipolar systems do provide estimates of the polarity of various RTILs, there can be circumstances when the steady state emission frequency of a dipolar system may not truly reflect the equilibrium solvation energy and, hence, the polarity of the medium. The fluorescence response of a dipolar system can be dependent on the excitation wavelength, an observation not commonly encountered in conventional solvents of similar polarities. On the other hand, the time-resolved fluorescence behavior of a dipolar solute in polar medium is one of the primary sources of information on the time-scale of reorganization of the solvent molecules around the photoexcited species. As the RTILs are sufficiently polar media, the time-dependent fluorescence data of the dipolar systems provide insight into the dynamics and mechanism of solvation in these media, which differ considerably from the conventional solvents. These aspects have been discussed taking into consideration the inherent absorption and fluorescence behavior of the imidazolium ionic liquids.     

Interactions between spiropyrans and room-temperature ionic liquids: photochromism and solvatochromism

A series of imidazolium-based room-temperature ionic liquids (RTILs) containing anions from organic carboxylic acids were prepared. A set of dye probes, including Reichardt's dye (30), 4-nitrioaniline, and N, N-diethyl-4-nitroaniline, were used to determine the ET(30) scales and the Kamlet-Taft parameters (pi*, alpha, and beta) of the RTILs. On the basis of the polarity properties, these RTILs were categorized into three groups: group A with beta >0.9, alpha <0.9; group B with beta <0.9, alpha <0.9; and group C with beta <0.9, alpha >0.9. Interactions of these RTILs with four photochromic spiropyran derivatives (SP-I, SP-II, SP-III, and SP-IV) were investigated. It was found that the spiropyrans could present photochromism (positive or negative) or not, depending mainly on the polarity properties of the RTILs and also on the structure itself. A new spectroscopic method based on the molecular transition energy of the spiropyran probes (ESP) was proposed to determine the polarity of those protic or fluorine-containing RTILs, which were failed with the Reichardt's dye (30) probe.     

How ionic are room-temperature ionic liquids? An indicator of the physicochemical properties

Room-temperature ionic liquids (RTILs) are liquids consisting entirely of ions, and their important properties, e.g., negligible vapor pressure, are considered to result from the ionic nature. However, we do not know how ionic the RTILs are. The ionic nature of the RTILs is defined in this study as the molar conductivity ratio (Lambda(imp)/Lambda(NMR)), calculated from the molar conductivity measured by the electrochemical impedance method (Lambda(imp)) and that estimated by use of pulse-field-gradient spin-echo NMR ionic self-diffusion coefficients and the Nernst-Einstein relation (Lambda(NMR)). This ratio is compared with solvatochromic polarity scales: anionic donor ability (Lewis basicity), E(T)(30), hydrogen bond donor acidity (alpha), and dipolarity/polarizability (pi), as well as NMR chemical shifts. The Lambda(imp)/Lambda(NMR) well illustrates the degree of cation-anion aggregation in the RTILs at equilibrium, which can be explained by the effects of anionic donor and cationic acceptor abilities for the RTILs having different anionic and cationic backbone structures with fixed counterparts, and by the inductive and dispersive forces for the various alkyl chain lengths in the cations. As a measure of the electrostatic interaction of the RTILs, the effective ionic concentration (C(eff)), which is a dominant parameter for the electrostatic forces of the RTILs, was introduced as the product of Lambda(imp)/Lambda(NMR) and the molar concentration and was compared with some physical properties, such as reported normal boiling points and distillation rates, glass transition temperature, and viscosity. A decrease in C(eff) of the RTILs is well correlated with the normal boiling point and distillation rate, whereas the liquid-state dynamics is controlled by a subtle balance between the electrostatic and other intermolecular forces.     

New innovations in ionic liquid–based miniaturised amperometric gas sensors

Gas detection is an essential part of everyday life; for some applications, using sensors for toxic and hazardous gases can literally mean the difference between life and death. In this minireview, recent progress in amperometric gas sensing using miniaturised electrodes and devices is described. The focus is on the use of nonvolatile room-temperature ionic liquids (RTILs) as electrolytes, which possess inherent advantages such as wide electrochemical windows, high thermal and chemical stability, intrinsic conductivity and good solvating properties. Various different gases, electrodes and RTILs have been investigated in the strive towards new materials for improved gas sensors. The most recent developments using porous membrane electrodes, planar devices (e.g. screen-printed, thin-film, microarray and interdigitated electrodes) and the modification of these surfaces for improved sensitivity are described. RTILs have great potential to be used as electrolytes in amperometric gas sensors, with improved lifespan of the sensor in hot/dry environments and allowing miniaturisation of devices. However, it is clear that more understanding of their long-term operation and utility in real environments (e.g. background air, varying temperatures and humidity levels) is needed before their realisation in successful commercial devices.     

Probing the Local Structure of Pure Ionic Liquid Salts with Solid‐ and Liquid‐State NMR

Room‐temperature ionic liquids (RTILs) are gaining increasing interest and are considered part of the green chemistry paradigm due to their negligible vapour pressure and ease of recycling. Evidence of liquid‐state order, observed by IR and Raman spectroscopy, diffraction studies, and simulated by ab initio methods, has been reported in the literature. Here, quadrupolar nuclei are used as NMR probes to extract information about the solid and possible residual order in the liquid state of RTILs. To this end, the anisotropic nature and field dependence of quadrupolar and chemical shift interactions are exploited. Relaxation time measurements and a search for residual second‐order quadrupolar coupling were employed to investigate the molecular motions present in the liquid state and infer what kind of order is present. The results obtained indicate that on a timescale of ～10^?8 sec or longer, RTILs behave as isotropic liquids without residual order.     

"Nonsolvent" applications of ionic liquids in biotransformations and organocatalysis

The application of room-temperature ionic liquids (RTILs) as (co)solvents and/or reagents is well documented. However, RTILS also have "nonsolvent" applications in biotransformations and organocatalysis. Examples are the anchoring of substrates to RTILs; ionic-liquid-coated enzymes (ILCE) and enzyme-IL colyophilization; the construction of biocatalytic ternary reaction systems; the combination of enzymes, RTILs, membranes, and (bio)electrochemistry; and ionic-liquid-supported organocatalysts. These strategies provide more robust, more efficient, and more enantioselective bio- and organocatalysts with many practical applications. As shown herein, RTILs offer a wide range of promising alternatives to conventional chemistry.     

离子液体在无机纳米材料合成上的应用

室温离子液体作为一种新型的绿色环保溶剂,在无机纳米材料合成中的应用引起越来越多研究者的注意。目前,已经利用室温离子液体合成出了纳米多孔材料、纳米粒子和中空球、一维纳米材料等。与传统的溶剂相比,离子液体在合成过程中体现出了很多优势,且合成的产物也不同,为无机纳米材料的合成开辟了一条新途径。本文就近年来国内外相关研究进展,对离子液体在无机纳米材料合成中的应用进行综述。     

Raman spectroscopic study on the solvation of N,N-dimethyl-p-nitroaniline in room-temperature ionic liquids

Electronic absorption spectra and Raman spectra of N,N-dimethyl-p-nitroaniline (DMPNA) have been measured in various fluids from the gaseous-like conditions in supercritical fluids (SCFs) to highly polar room-temperature ionic liquids (RTILs). We found that the S0-S1 absorption band center of DMPNA in RTILs is mostly determined by the molar concentrations of ions. On the other hand, the bandwidth of the absorption spectrum does not follow the expectation from a simple dielectric continuum model. Especially in SCFs, the bandwidth of the absorption spectrum decreases with increasing solvent density, suggesting that the intramolecular reorganization energy is a decreasing function of the solvent density. The Raman shift of the NO2 stretching mode has been proven to be a good indicator of the solvent polarity; i.e., the vibrational frequency of the NO2 stretching mode changes from 1340 cm-1 in mostly nonpolar solvent such as ethane to 1300 cm-1 in water. The linear relationship between the absorption band center and the vibrational frequency of the NO2 mode, which was observed for conventional liquids in a previous paper (Fujisawa, T.; Terazima, M.; Kimura, Y. J. Chem. Phys. 2006, 124, 184503), holds almost well for all fluids including SCFs and RTILs. On the other hand, the vibrational bandwidth does not show a simple relationship with the absorption band center. The vibrational bandwidths in RTILs are generally larger in comparison with those in conventional liquids with similar polarity scales. Among the RTILs we investigated, the vibrational bandwidth loosely correlates with the molecular size of the anion. A similar dependence on the anion size is also observed for the bandwidth of the absorption spectrum. We have also investigated the excitation wavelength dependence of the Raman shift of the NO2 stretching mode in RTILs. The extent of the dependence on the excitation wavelength in all fluids is well correlated with the vibrational bandwidth.     

Effect of Cosolvent on Bulk and Interfacial Characteristics of Imidazolium Based Room Temperature Ionic Liquids

Here we report a systematic study on electrical conductivity and surface tension of various concentrated solutions of imidazolium based room temperature ionic liquids (RTILs), viz. 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][ $\hbox {PF}_{6}$ ]) and 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][ $\hbox {BF}_{4}$ ]) in the cosolvents methanol and acetonitrile at 298.15 K. The aim of the investigations was to explore the impact of cosolvents on bulk and interfacial characteristics of imidazolium based RTILs. It was observed that both methanol and acetonitrile mix non-ideally with and enhance the transport parameters of the imidazolium based RTILs. An interesting outcome of the presented work is that the investigated RTILs retain their inherent structural characteristics up to a high dilution limit with cosolvent, and this limit is higher in acetonitrile than in methanol as cosolvent. The findings establish that, in comparison to methanol, acetonitrile is a better cosolvent that can be used for enhancing the transport parameters of imidazolium based RTILs for electrochemical and other applications. The results are explained in light of structure-composition-property relations and ion-ion and ion-cosolvent interactions.     

室温离子液体在分离科学研究中的新进展

室温离子液体作为一种重要的绿色溶剂,由于在金属离子、小分子有机物的萃取分离,气体吸附分离以及作为液相和气相色谱固定相等许多分离过程中体现出高分离效率和高选择性的特点,正在成为分离科学研究的前沿领域.着重总结了从2003—2006年的室温离子液体在分离科学领域中的新进展,并对其应用领域和发展前景做了展望.提出进一步加强离子液体的功能化和固定化技术及其在分离科学中的应用基础研究,探索离子液体有效的回收和再循环利用的新方法,是离子液体今后在分离科学研究中的一系列重要内容.     

离子液体微乳液体系的应用研究

室温离子液体具有诸多优异的物理化学性质及功能,是一类备受关注的新型介质和材料,应用于诸多领域。特别是近年来,由离子液体参与形成的微乳液因其在生物、医药、催化以及材料制备等领域具有潜在的应用前景而备受关注。本文综述了近年来咪唑类离子液体作为极性、非极性和表面活性剂组分,分别取代微乳液体系中的水相、油相和表面活性剂相,形成的一系列新型的微乳液体系的研究进展,归纳了水、有机溶剂、高聚物、助表面活性剂、温度等因素对离子液体微乳液性质的影响。重点介绍了离子液体微乳液的热点应用,包括以离子液体微乳液液滴为模板合成纳米材料,离子液体微乳液作为酶反应的介质及其在有机反应等方面的研究进展。     

What makes ionic fluids characteristically ionic? A corresponding-states analysis of the surface tension of an ionic model fluid with variable dispersion interactions

Inorganic molten salts, such as NaCl, are known to show characteristically lower values of Guggenheim's corresponding-states surface tension γ(red) at a given reduced temperature T∕T(c) than simple or aprotic polar fluids. Recently, the corresponding values of γ(red) for (some) room temperature ionic liquids (RTILs) were found in the same region as those for weakly polar fluids, that is, markedly above the values typical of inorganic molten salts despite the ionic character of RTILs. Here, we present the results of simulations of an ionic model fluid in which the strength of attractive dispersion interactions among the ions is varied relative to the Coulomb interactions. For weak dispersive interactions, the behavior known for real inorganic molten salts is found. If the attractive dispersion energy of two unlike ions at contact exceeds 20% of the Coulombic attraction in such an isolated ion pair, γ(red) increases markedly and approaches the region of values for simple and polar fluids. Rough theoretical estimates of the relative strengths of dispersive and Coulombic attractions in molten inorganic salts and in RTILs support our conclusion that the dispersion interactions in RTILs are strong enough for their corresponding-states surface tension to behave regularly and, thus, to deviate from the values one would expect for strongly ionic systems.     

Transport properties of room-temperature ionic liquids from classical molecular dynamics

Room-temperature ionic liquids (RTILs) have attracted much attention in the scientific community in the past decade due their novel and highly customizable properties. Nonetheless, their high viscosities pose serious limitations to the use of RTILs in practical applications. To elucidate some of the physical aspects behind transport properties of RTILs, extensive classical molecular dynamics calculations are reported. Here, in particular, bulk viscosities and ionic conductivities of butyl-methyl-imidazole based RTILs are presented over a wide range of temperatures. The dependence of the properties of the liquids on simulation parameters, e.g., system-size effects or the choice of the interaction potential, is analyzed in detail.     

Intermolecular interaction-induced hierarchical transformation in 1D nanohybrids: analysis of conformational changes by 2D correlation spectroscopy

We have examined both self-assembly and confinement effect in room-temperature ionic liquid (RTIL)-aluminum hydroxide hybrids (RAHs) to attain a fundamental understanding of special phenomena in nanoscale spaces as well as to design functional nanomaterials for practical applications. Phase-controlled one-dimensional (1D) RAHs were synthesized through a simple ionothermal process. The RAHs were hierarchically transformed in terms of the molecular structures, morphologies, and phases of the materials during the ionothermal process with respect to the concentration of RTIL. In addition to the hierarchical transformation, the RTIL/aluminum hydroxide nanohybrids revealed unexpected physical behaviors, including thermal transition variation of the RTIL in confined environments and a phase transition from nanosolid to nanoliquid affected by changes of the melting points. More importantly, intermolecular interaction induced-self-assembly and confinement effect of RTILs inside an integrated hybrid system, which have not been clearly explained to date, were analyzed by 2D infrared correlation spectroscopy (2D IR COS); dynamic behaviors of RTILs, i.e., sequentially spatial reorientation and kinetically conformational changes, were attributed to the interactions between RTILs and aluminum hydroxides. 2D IR COS offers a new way to interpret highly complex, veiled systems such as the formation mechanism of nanoparticles, biomineralization, self/supramolecular assembly, and nanoconfinement.     

Why are viscosities lower for ionic liquids with -CH2Si(CH3)3 vs -CH2C(CH3)3 substitutions on the imidazolium cations?

We have prepared novel room temperature ionic liquids (RTILs) with trimethylsilylmethyl (TMSiM)-substituted imidazolium cations and compared the properties of these liquids with those for which the TMSiM group is replaced by the analogous neopentyl group. The ionic liquids are prepared with both tetrafluoroborate (BF(4)(-)) and bis(trifluoromethylsulfonyl)imide (NTf(2)(-)) anions paired with the imidazolium cations. At 22 degrees C, the TMSiM-substituted imidazolium ILs have shear viscosities that are reduced by a factor of 1.6 and 7.4 relative to the alkylimidazolium ILs for the NTf(2)(-) and BF(4)(-) anions, respectively. To understand the effect of silicon substitution on the viscosity, the charge densities have been calculated by using density functional theory electronic structure calculations. The ultrafast intermolecular, vibrational, and orientational dynamics of these RTILs have been measured by using femtosecond optical heterodyne-detected Raman-induced Kerr effect spectroscopy (OHD-RIKES). The intermolecular dynamical spectrum provides an estimate of the strength of interactions between the ions in the RTILs, and provides a qualitative explanation for the observed reduction in viscosity for the silicon-substituted RTILs.     

Naphthalene‐Functionalized,Photoluminescent Room Temperature Ionic Liquids Bearing Small Counterions

Obtaining π‐conjugated room temperature ionic liquids (RTILs) is difficult because of the relatively strong π–π interaction among the π‐moieties. Existing strategies by using bulky counterions greatly hindered further property optimization and potential applications of these intriguing functional fluids through simple ion exchange. Herein, four naphthalene‐functionalized, π‐conjugated RTILs with small counterions (Br^?) have been facilely synthesized with high yields. Our strategy is to attach branched alkyl chains to the cationic backbone of the target compounds ( 2 a – d ), which effectively tune inter‐ and intramolecular interactions. Compounds 2 a – d have satisfactory thermal stability (up to 300 °C) and low melting points (<?19 °C). Rheological measurements revealed the fluid character of 2 a – d , whose viscosity decrease with the increase of the alkyl chain length and temperature. The presence of the π‐conjugated naphthalene moiety imparts 2 a – d photoluminescent properties in bulk solutions. Moreover, the absence of strong π–π stacking among the naphthalene units in solvent‐free states enables them to be used as a new generation of photoluminescent inks.     

Determination of the polarities of some ionic liquids using 2-nitrocyclohexanone as the probe

Solute-solvent interactions on the keto-enol tautomerism of 2-nitrocyclohexanone in several organic solvents and room-temperature ionic liquids (RTILs) have been analyzed in terms of multiparameter equations. Permittivity and cohesive pressure values of the RTILs, unavailable by direct measurements, have been derived.     

Understanding the wettability of nanometer-thick room temperature ionic liquids (RTILs) on solid surfaces

Many important applications of room temperature ionic liquids(RTILs), e.g., lubrication, energy storage and catalysis, involve RTILs confined to solid surfaces. In order to optimize the performance, it is critical to understand the wettability of nanometer-thick RTILs on solid surfaces. In this review, the recent progress in this filed is presented. First, the macroscopic wettability of RTILs on solids will be discussed briefly.Afterwards, the wetting of nanometer-thick RTILs will be discussed with the emphasis on RTIL/mica and RTIL/graphite interfaces since mica and graphite not only are mostly studied but also have important real-life applications. For RTIL/mica interface, the extended layering that promotes the wetting has been extensively reported and it is generally accepted that the electrostatic interaction at the RTIL/mica interface is the key. However, recent works from others and us highlight the unexpected effect of water:Water enables ion exchange between K+and the cations of RTILs on the mica surface and thus triggers the ordered packing of cations/anions in RTILs, resulting in extended layering. Different from mica, there is no electrical charge on the graphite surface. Interestingly, previous reports showed inconsistent results on the wettability of RTILs on graphite. Recent research from others and us suggested that π-π~+stacking between sp~2 carbon and the imidazoliumcation in the RTILs is the key to the extended layering and enhanced wettability of RTILs. Lastly, the future research directions will be briefly discussed.